The 2015 National Building Code of Canada (NBC) brought about multiple changes. One of the most important from an insulation standpoint is the treatment of the language concerning RSI values. (Although most in the construction industry are more familiar with the term ‘R-value,’ this article will use the metric values RSI for insulation.)

When designers are deciding which insulation products to specify for a given project, two questions come to mind: ‘What is the R-value?’ and ‘What is the permeance?’ The answer to both these queries is, ‘It is all relative.’

The Polyisocyanurate Insulation Manufacturers Association (PIMA) developed a research report in response to recent articles questioning the thermal performance of polyiso roof insulation in colder climates. According to “Thermal Resistance and Mean Temperature: A Report for Building Owners and Design Professionals,” polyiso roof insulation R-value shows no significant variation among North American climate zones.

On the surface, R-value is a simple thing. In fact, it has become the standard metric of thermal performance precisely because it is easy to explain and understand. Most insulation materials have ‘label R-values’ stamped on their faces (or at least displayed in large print on the packaging), but these values do not tell the whole story of how insulation performs in service. Some complicating factors—such as thermal bridging—have become fairly well-known.

With the ever-increasing demand for efficiency in new buildings, as well as the retrofitting of existing facilities, exterior sheathing plays an integral role in reducing energy consumption and the associated carbon dioxide (CO2) emissions. (This article deals with insulating, not structural, sheathing). Exterior insulation, continuous across all structural members without thermal bridges (other than fasteners and service openings), is the most thermally effective way to insulate a building. The sheathing’s thickness depends on the climate zone.

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